Syntheses, structure and ethylene polymerization behavior of β-diiminato titanium complexes

A series of new titanium complexes bearing β-diiminato ligands [(Ph)NC(R1)CHC(R2)N(Ph)]2TiCl2 (4a: R1 = R2 = CH3; 4b: R1 = R2 = CF3; 4c: R1 = Ph, R2 = CH3; 4d: R1 = Ph, R2 = CF3) has been synthesized and characterized. X-ray crystal structures reveal that complexes 4a and 4c adopt distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4a–d are active catalysts for ethylene polymerization, and produce high molecular weight polyethylenes. Catalyst activities and the molecular weights of polymers are considerably influenced by the steric and electronic effects of substituents on the catalyst backbone under the same polymerization condition. With the strong electron-withdrawing groups (CF3) at R1 or/and R2 position, complexes 4b and 4d show higher activities than complexes 4a and 4c, respectively.

Graphical abstractA series of new titanium complexes [(Ph)NC(R1)CHC(R2)N(Ph)]2TiCl2 has been synthesized and characterized, and is shown to be active catalysts for ethylene polymerization.Figure optionsDownload full-size imageDownload as PowerPoint slide